Before you begin cooking, prepare all of the vegetables. Mince the garlic, dice the onion, chop the celery into small pieces, peel and slice the carrot, and break the green beans into one inch sections. If your mushrooms aren’t pre-sliced, go ahead and slice them.
Add the vegetable oil, onion, and garlic to a large pot. Saute over medium heat until the onions have softened. Add the mushrooms and continue to saute until the mushrooms have released all of their moisture, become limp, and turned dark tan in color.
Melt the butter into the pot. Once the butter has melted, add the flour. Stir and cook this mixture for about three minutes. It’s okay if the flour begins to coat the bottom of the pot, but if it looks like it may begin to burn, turn off the heat.
Warm the vegetable broth slightly in the microwave. Add the broth to the pot and stir to dissolve all of the flour off of the bottom of the pot and off of the vegetables. Warm the milk in the microwave. Slowly add the milk while stirring.
Add the rest of the vegetables (green beans, carrots, celery, corn, peas) and the thyme. Increase the heat and bring the pot up to a simmer. Once it reaches a simmer, reduce the heat to medium-low and allow it to simmer for 10-15 minutes while you prepare the biscuit dough. Stir the mixture occasionally to prevent it from scorching on the bottom of the pot.
Preheat the oven to 450 degrees. While the vegetables are cooking, prepare a basic biscuit dough. The recipe and step by step instructions can be found here. This will only take about 10 minutes.
After simmering for 10-15 minutes, the liquid in the pot should have reduced and thickened. If you’d like it thicker, you can sprinkle in about a teaspoon of cornstarch and stir until thickened. Give it a taste and add salt and pepper to your liking (I added about 3/4 tsp of salt). Pour the vegetable mixture in the bottom of an 8×8 inch casserole dish.
Turn the biscuit dough out onto a floured surface and shape it into a large square, approximately the same size and shape as the casserole dish. Transfer the biscuit dough to top the vegetables in the dish. Use a sharp knife to cut a few slits in the biscuit dough to allow steam to escape. Bake the dish in the preheated oven for 15-17 minutes or until the biscuit is golden brown on top.